This invention relates to the assembly of nuclear fuel elements and particularly to the automatic assembly of nuclear fuel elements employing mixed oxide fuels.
In many designs of nuclear reactors, the reactor vessel has an inlet and an outlet for circulation of a coolant in heat transfer relationship with a core contained therein that produces heat. The core comprises an array or arrays of fuel assemblies which contain fuel elements. The fuel element is generally a cylindrical metallic sheath sealed at both ends containing nuclear fuel. The nuclear fuel which may be, for example, ceramic fuel pellets of a uranium compound is stacked in the fuel elements. During reactor operation, the nuclear fuel pellets decompose releasing fission products such as fission gas while generating heat in a manner well known in the art. The reactor coolant absorbs the heat while circulating through the core thereby cooling the fuel elements of the core and heating the coolant. Of course, the heated coolant may then be used to produce power in a conventional manner.
There are several methods known in the art for loading uranium fuel pellets into the cylindrical metallic sheath for use in a light water reactor. One such method comprises simply placing the fuel pellets in the metallic sheath by hand. This method is possible because non-irradiated uranium fuel does not pose serious radiological problems to working personnel. However, when the nuclear fuel utilized is of a more toxic nature such as plutonium or a reprocessed uranium compound, then increased safeguards must be employed to prevent releasing radioactive contaminants to the atmosphere and to prevent overexposing working personnel. When such toxic fuel is employed, it is known in the art to use glove box handling techniques to load the fuel pellets into the metallic sheath.
Typical glove box handling procedure first requires transferring the nuclear fuel pellets in a sealed container into the glove box and then firmly sealing the glove box. Once placed in the glove box, the sealed container may then be opened by manual gloved manipulation. The fuel pellets may then be loaded into a metallic sheath either totally enclosed within the glove box, or with its open end sealed into a glove box through a plastic membrane. When the metallic sheath has thus been filled to the proper level with fuel pellets, the fuel element must then be placed in a sealed container or its contaminated open end sealed off in order to be moved to the next glove box where the next procedure can be performed such as welding the end plug on the metallic sheath. The process of tranferring the material and components from one glove box to the next can be quite time consuming and thus renders such procedures unacceptable from a mass production standpoint.
An example of an arrangement for transferring nuclear fuel elements into a glove box enclosure is described in U.S. Pat. No. 3,711,993 to J. Liesch et al, issued Jan. 23, 1973. The Liesch patent discloses a cylindrical chamber disposed in an isolation wall between a contaminated and an uncontaminated area for providing a passageway therebetween. The chamber is enclosed between a pair of shutters with variable apertures that allow the passage of a nuclear fuel element therethrough. The chamber may be flushed or purged with a gas so as to entrain contaminated particles in the gas which may then be conducted through a filter located remote from the chamber thereby trapping the contaminated particles in the filter. The patent to Liesch indicates that such a filter may be of the electrostatic or activated carbon type. While the Liesch patent describes a particular arrangment for transferring a nuclear fuel element into or out of a glove box type enclosure, it along with the other prior art does not solve the problem of automatically transferring nuclear fuel elements between assembly stations on a mass production basis without releasing contaminants into the atmosphere.